The present invention relates to bellows of a type which is elastically extensible and compressible along a defined axis, comprising a wall which is arranged around the axis and which, when it is viewed in section through any half-plane including the axis, comprises a plurality of substantially identical waves which are mutually adjacent parallel to the axis and each of which generally, that is to say with local exceptions especially at the extremities of the bellows, comprises two flexible sidewalls connected together by a comparatively rigid rounded peak, which is convex in the outward direction with respect to the axis, and each of which is connected to a sidewall of a respective adjacent wave by a comparatively rigid rounded trough which is convex in the inward direction with respect to the axis, the bellows being especially capable of taking up a defined state of elastic axial contraction just sufficient for each sidewall to be at least approximately contiguous on the one hand with the other sidewall of the same wave, at a defined point comparatively close to the axis, and on the other hand with a sidewall of a respective adjacent wave, at a defined point comparatively distant from the axis, while defining in proximity to each peak a defined mean peak direction and in immediate proximity to each trough, a defined mean trough direction.